U.S. patent number 5,382,954 [Application Number 08/068,337] was granted by the patent office on 1995-01-17 for resolution advisory display instrument for tcas guidance.
This patent grant is currently assigned to Honeywell Inc.. Invention is credited to Donald F. Fenstermaker, Thomas W. Kennedy, Jr..
United States Patent |
5,382,954 |
Kennedy, Jr. , et
al. |
January 17, 1995 |
Resolution advisory display instrument for TCAS guidance
Abstract
An aircraft indicating system for displaying a resolution
advisory signal from a Traffic Advisory and Collision Avoidance
System provides an indicating pitch attitude symbol to the pilot
engendering an instinctive response to avoid a collision. A driving
circuit converts a TCAS signal in the form of a vertical speed
command to a pitch command for energizing the indicating symbol by
effecting a vertical displacement thereof in accordance with the
guidance resolution advisory. The display signal is generated in
accordance with the relationship: ##EQU1## where: .PHI.=aircraft
roll attitude, limited to + or - 30.degree. .THETA..sub.CMD
=commanded pitch attitude defining the upper and lower pitch limits
of the resolution advisory symbology .THETA..sub.EXIST =current
pitch angle V.sub.ZTCAS =TCAS vertical speed command V.sub.ZEXIST
=current vertical speed V.sub.T =true airspeed K=conversion
constant.
Inventors: |
Kennedy, Jr.; Thomas W.
(Phoenix, AZ), Fenstermaker; Donald F. (Glendale, AZ) |
Assignee: |
Honeywell Inc. (Minneapolis,
MN)
|
Family
ID: |
22081916 |
Appl.
No.: |
08/068,337 |
Filed: |
May 27, 1993 |
Current U.S.
Class: |
340/961; 701/301;
342/29 |
Current CPC
Class: |
G01C
23/005 (20130101); G01S 13/933 (20200101) |
Current International
Class: |
G01C
23/00 (20060101); G01S 13/00 (20060101); G01S
13/93 (20060101); G08G 005/04 () |
Field of
Search: |
;340/961,973,975 ;342/29
;364/461 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
3614728 |
October 1971 |
Borrok et al. |
3691520 |
September 1972 |
Nordstrom |
4860007 |
August 1989 |
Konicke et al. |
4980683 |
December 1990 |
O'Sullivan et al. |
5185606 |
February 1993 |
Verbaarschot et al. |
5248968 |
September 1993 |
Kelly et al. |
|
Primary Examiner: Swarthout; Brent
Attorney, Agent or Firm: Albin; A. L. Jepsen; D. E.
Champion; R. E.
Claims
We claim:
1. An aircraft indicating system for displaying a resolution
advisory signal for avoiding a collision between first and second
aircraft, comprising:
means for receiving a TCAS resolution advisory signal in the form
of a vertical speed command for determining the evasive action to
be taken by the pilot of the first aircraft to avoid collision with
the second aircraft,
means for receiving signals corresponding to the aircraft roll
angle and current pitch angle,
means for receiving signals corresponding to the current vertical
speed and true airspeed,
means for applying said TCAS signal, said current vertical speed
signal, and said true airspeed signal to generate a signal
corresponding to a first trigonometric function,
means for deriving a second trigonometric function representative
of aircraft roll angle and for generating a corresponding signal
thereof,
means for combining said first and second trigonometric function
signals to derive a further signal representative of a desired
change in aircraft pitch angle,
means for combining said current pitch angle signal and said
desired change in pitch angle signal to provide a signal
corresponding to a commanded pitch angle for avoiding said
collision, and
means for applying said commanded pitch angle signal to electronic
display means for providing a symbolic representation thereof.
2. An aircraft indicating system as set forth in claim 1, further
comprising:
first summing junction means responsive to said TCAS signal and
said current vertical speed signal for providing an algebraic
difference signal thereof,
first divisor means responsive to said algebraic difference signal
and said true airspeed signal for providing a first quotient signal
by dividing said algebraic difference signal by said true airspeed
signal,
said first trigonometric function adapted for providing a signal
proportional to the angle corresponding to the inverse
trigonometric sine of said first quotient signal,
said second trigonometric function adapted for providing a signal
proportional to the trigonometric cosine of said roll angle
signal,
second divisor means responsive to said first and second
trigonometric functions for providing a second quotient signal by
dividing a signal corresponding to said first trigonometric
function by a signal corresponding to said second trigonometric
function, and
second summing junction means for providing an algebraic sum of
said second quotient signal and said pitch angle signal,
said algebraic sum defining said commanded pitch angle signal.
3. A system as set forth in claim 2, further comprising roll angle
limiting means, disposed between a source of said roll angle signal
and said means for deriving a second trigonometric function, for
limiting said roll angle signal between first and second
predetermined limits.
4. A system as set forth in claim 3, wherein said first and second
predetermined limits correspond to plus or minus 30 degrees.
5. A system as set forth in claim 4, wherein said desired change in
pitch angle signal is applied to a rolling average filter and
outputs thereof are comprised of a plurality of successive pitch
angle signals sequentially averaged over a predetermined number of
display frames, successive outputs of said filter being
periodically updated at each display frame, thereby to preclude
transient disturbances due to air turbulence.
6. A system as set forth in claim 5, wherein said plurality of
successive pitch angle signals are averaged over at least four
display frames.
7. A system as set forth in claim 2, wherein said symbolic
representation is defined by the relationship: ##EQU3## where:
.PHI.=aircraft roll attitude, limited to + or -30.degree., in
degrees
.PHI..sub.CMD =commanded pitch attitude defining the upper and
lower pitch limits of the resolution advisory symbology, in
degrees
.PHI..sub.EXIST =current pitch angle, in degrees
V.sub.ZTCAS =TCAS vertical speed command, in ft/min
V.sub.ZEXIST =current vertical speed, in ft/min
V.sub.T =true airspeed, in knots
K=conversion constant
8. A system as set forth in claim 7, wherein said display means
comprises an aircraft display instrument of the integrated primary
flight display type,
said display means defining a display field of view having a
vertical axis, an index in the form of an aircraft symbol
relatively fixed with respect to said display field of view and
generally disposed in the center of said field, a horizon defining
reference line responsive to the roll and pitch attitude of said
aircraft for correspondingly positioning said horizon line relative
to said index, a first plurality of reference symbols
circumferentially disposed with respect to said vertical axis and
indicative of roll attitude of said aircraft when one of said
reference symbols is aligned with said horizon line, and a second
plurality of reference symbols substantially orthogonally disposed
with respect to said horizon line and indicative of the pitch
attitude of the aircraft,
wherein said symbolic representation comprises at least first and
second indicia superposed on said field of view and assuming
priority over any underlying indicia, said first indicia indicative
of a target pitch command to climb or descend and said second
indicia indicative of a proscribed pitch maneuver region in
accordance with a given guidance resolution advisory, said first
and second indicia responsive to said commanded pitch angle signal
to effect vertical displacement of said indicia for command
purposes,
said first indica comprised of a horizontal band of a first
predetermined color, said band disposed with respect to said
vertical axis in accordance with said commanded pitch angle signal
and having a vertical depth corresponding to a target range of
acceptable pitch deviation in accordance with the upper and lower
bounds of said given resolution advisory,
said second indicia comprised of a pair of angularly disposed
display lines of a second predetermined color and terminating at
respective ends of said horizontal band, said first and second
indicia defining an open-ended relatively trapezoidal symbol, said
open end having a horizontal dimension exceeding the longitudinal
dimension of the closed end defined by said horizontal bar, said
open end downwardly disposed in response to a resolution advisory
command to climb and upwardly disposed in response to a resolution
advisory command to descend.
9. A system as set forth in claim 8, further comprising a third
indicia substantially in the form of said second indicia
symmetrically disposed with respect to said vertical axis and
oppositely disposed with respect to the symbol defined by said
first and second indicia, said first and second indicia being
responsive to a resolution advisory with respect to a first threat
aircraft and said third indicia responsive to a resolution advisory
with respect to a second threat aircraft.
10. A system as set forth in claim 9, further comprising a fourth
indicia responsive to said TCAS resolution advisory signal and
superposed laterally of at least said first and second indicia on
said display field of view and proximate to a numerical readout of
current vertical speed,
said fourth indicia comprising a vertical bar having a first sector
of a first given color indicative of a commanded vertical speed and
variable in vertical displacement with respect to a plurality of
reference marks indicative of vertical speed,
said vertical bar further comprising at least a second sector of a
further given color, said second sector extending substantially
from said first sector to a predetermined one of said plurality of
reference marks indicative of vertical speed, said second sector
disposed above or below said first sector in accordance with a
proscribed vertical speed range defined by said resolution advisory
signal.
11. A method for displaying a guidance resolution advisory in the
form of pitch attitude command symbology superposed on an aircraft
display instrument of the integrated primary flight display type,
comprising:
providing a TCAS resolution advisory signal in the form of a
vertical speed command for determining the evasive action to be
taken by the pilot of a first aircraft to avoid collision with a
second aircraft,
providing signals corresponding to the aircraft roll angle and
current pitch angle,
providing signals corresponding to the current vertical speed and
true airspeed,
applying said TCAS signal, said current vertical speed signal, and
said true airspeed signal to generate a signal corresponding to a
first trigonometric function,
deriving a second trigonometric function representative of aircraft
roll angle and generating a corresponding signal thereof,
combining said first and second trigonometric function signals to
derive a further signal representative of a desired change in
aircraft pitch angle,
combining said current pitch angle signal and said desired change
in pitch angle signal to provide a signal corresponding to a
commanded pitch angle for avoiding said collision, and
applying said commanded pitch angle signal to said display
instrument to effect vertical displacement of a symbolic
representation thereof for command purposes.
Description
BACKGROUND OF THE INVENTION
1. Field of The Invention
The invention relates to indicating instruments, and more
particularly to a primary flight director instrument having a pitch
cue responsive to resolution advisory guidance commands for
collision avoidance.
2. Description of The Prior Art
The Traffic Advisory and Collision Avoidance System (TCAS) uses a
Mode S Transponder with which civilian and military aircraft are
equipped to communicate collision avoidance decisions between
aircraft. One form of TCAS, known as TCAS II, is intended for large
commercial and general aviation aircraft. Aircraft in proximity are
tracked in both the horizontal and vertical planes, from which the
time of closest approach may be predicted. However, the lack of
adequate bearing measurement accuracy precludes support of
horizontal maneuvers. The pilot of the own aircraft is advised on
how to avoid a collision with respect to advisories to climb,
descend, do not climb, or do not descend, and may also be advised
as to a required vertical speed rate to avoid a collision. If the
threat aircraft is also equipped with a TCAS system, the avoidance
maneuver will be communicated and coordinated with the threat
aircraft accordingly, so that both aircraft do not select the same
avoidance maneuver.
Threat detection is performed at two levels. When air traffic
approaches within a predetermined protective volume a traffic
advisory is provided to alert the pilot to attempt a visual
sighting and take whatever corrective action he deems appropriate
to increase separation between the aircraft. If the two aircraft
continue to approach, typically such that within a minimum time of
20 seconds they will be within 0.1 nautical mile (n) of each other
and with an altitude difference not greater than 750 ft, a
resolution advisory will be issued, displaying a maneuver to the
pilot to increase separation of the aircraft. The advisories may be
accompanied by limits to the rate of climb or descent.
Prior art resolution advisory displays have been in the form of a
mechanical instrument or electronic display providing a pointer on
an altitude rate scale and an arrow or colored scale for displaying
change in altitude advisories. See, for example, U.S. Pat. No.
4,914,733 and U.S. Pat. No. 3,621,210. However, such displays have
heretofor not provided command information for changes in pitch
attitude necessary to satisfy the resolution advisory.
Aircraft primary flight director instruments are well known for use
in providing visual commands to the pilot. Thrust, pitch attitude,
and bank attitude controls are exercised by the human pilot while
observing the flight director display. When the pilot manipulates
the aircraft controls in a manner to keep the steering cues aligned
with corresponding fixed reference symbols, he will satisfy the
pitch and roll attitude control law so that the aircraft is
maintained on a predetermined flight path.
Such flight director steering cues have in general been provided in
two forms--steering bars, adapted for movement up or down to
command corresponding changes in pitch and for movement left or
right to command bank angle changes, and aircraft symbols,
representative of the attitude of the aircraft, which move up and
down to command pitch changes and roll left or right to command
bank angle changes.
The present invention provides an indicator for a primary flight
director instrument display which is provided with a single cue
provided in pitch to provide visual commands for bringing the craft
to a pitch attitude commensurate with the resolution advisory
vertical velocity signal. It overcomes the disadvantage of purely
performance cues such as vertical velocity, in which the
performance cue display may lag the current vertical speed.
A single cue provides both a pitch change command and indicates a
guarded region to be avoided. A further cue provides the current
vertical speed in a numerical display as well as bands indicating a
target vertical velocity and a proscribed vertical velocity range.
The instrument further provides the capability of indicating pitch
commands in the presence of two threat aircraft.
SUMMARY OF THE INVENTION
In accordance with the present invention an aircraft indicating
system for displaying a resolution advisory signal for avoiding a
collision between first and second aircraft comprises means for
receiving a TCAS resolution advisory signal in the form of a
vertical speed command for determining the evasive action to be
taken by the pilot of the first aircraft to avoid collision with
the second aircraft, means for receiving signals corresponding to
the aircraft roll angle and current pitch angle, means for
receiving signals corresponding to the current vertical speed and
true airspeed, means for applying the TCAS signal, current vertical
speed signal, and the true airspeed signal to generate a signal
corresponding to a first trigonometric function, means for deriving
a second trigonometric function representative of aircraft roll
angle and for generating a corresponding signal thereof, means for
combining the first and second trigonometric function signals to
derive a further signal representative of a desired change in
aircraft pitch angle, means for combining the current pitch angle
signal and the desired change in pitch angle signal to provide a
signal corresponding to a commanded pitch angle for avoiding a
collision, and means for applying the commanded pitch angle signal
to a display for providing a symbolic representation thereof.
In a preferred embodiment the invention comprises an aircraft
indicating system of the integrated primary flight display type,
the indicator defining a display field of view having a vertical
axis, an index in the form of an aircraft symbol relatively fixed
with respect to the display field of view and generally disposed in
the center of the field, a horizon-defining reference line
responsive to the roll and pitch attitude of the aircraft for
correspondingly positioning the horizon line relative to the index,
a first plurality of reference symbols circumferentially disposed
with respect to the vertical axis and indicative of roll attitude
of the aircraft when one of the reference symbols is aligned with
the horizon line, and a second plurality of reference symbols
substantially orthogonally disposed with respect to the horizon
line and indicative of the pitch attitude of the aircraft, wherein
the symbolic representation comprises a least first and second
indicia superposed on the field of view and assuming priority over
any underlying indicia, the first indicia indicative of a target
pitch command to climb or descend and the second indicia indicative
of a proscribed pitch maneuver region in accordance with a given
guidance resolution advisory, the first and second indicia
responsive to the commanded pitch angle signal to effect vertical
displacement of the indicia for command purposes, the first indicia
comprised of a horizontal band of a first predetermined color, the
band disposed with respect to the vertical axis in accordance with
the commanded pitch angle signal and having a vertical depth
corresponding to a target range of acceptable pitch deviation in
accordance with the upper and lower bounds of the given resolution
advisory, the second indicia comprised of a pair of angularly
disposed display lines of a second predetermined color and
terminating at respective ends of the horizontal band, the first
and second indicia defining an open-ended relatively trapezoidal
symbol, the open end having a horizontal dimension exceeding the
longitudinal dimension of the closed end defined by the horizontal
bar, the open end downwardly disposed in response to a resolution
advisory command to climb and upwardly disposed in response to a
resolution advisory command to descend.
The invention will be described more fully by way of example, with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a functional block diagram of the means for generating
the displays of FIGS. 2-3.
FIG. 2 is a front elevation view of the primary flight display
instrument of the present invention, showing the novel pitch
command indicia as responsive to an up resolution advisory.
FIG. 3 is a front elevation view of the primary flight display
instrument of the present invention, showing the pitch command
indicia for a down advisory in the presence of two threat
aircraft.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention may be described in terms of a collision
avoidance indicator in combination with aircraft vertical speed
indication. It is particularly adapted to flight instruments of the
electronics integrated display type, which may utilize a CRT in
raster or stroke scanning mode, or a combination thereof, or other
displays such as an active matrix type. Such an indicator system is
described, for example, in U.S. Pat. No. 4,149,148 assigned to the
assignee of the present invention. The means for generating such
displays are well known to those skilled in the art.
Referring to FIG. 1, a command signal V.sub.ZTCAS is provided by a
collision avoidance computer 10 in the form of a vertical speed
command. The present invention converts the TCAS vertical speed
command into a pitch command for display in a unique symbol on a
primary flight display instrument. The details of the computer are
not described herein, there being numerous configurations known to
the state of the art for formulating collision avoidance command
signals as aircraft climb or descent rates. The present invention
combines the vertical speed command with a pitch attitude indicator
to provide a display which conveys an instinctive pitch attitude
command to the pilot while minimizing the need for pilot
interpretation and minimizing reaction time.
The vertical speed command signal 10 is applied to an input of
summing junction 12. A conventional air data computer 14 provides a
signal V.sub.Z corresponding to the current vertical speed to
summing junction 12, where signals V.sub.ZTCAS and V.sub.Z are
algebraically combined in a subtractive manner, the difference
being applied to a first divider 16. Air data computer also
supplies a signal corresponding to true airspeed to divider 16. The
quotient of the difference signal on lead 18 divided by the true
airspeed signal on lead 20 is applied to a gain block 21, which
applies a multiplier factor K to the divider output to convert the
airspeed difference from ft/min to knots. The output of gain block
K is applied to trigonometric function block 22, which outputs a
signal on lead 24 representative of an angle corresponding to the
signal output of divider 16.
A conventional on-board inertial reference system 26 providing
pitch attitude and roll attitude signals provides a signal .PHI.
which is a measure of the roll attitude of the aircraft. The signal
.PHI. on lead 28 is coupled to a limiter 30, which limits the
output to a maximum of plus or minus 30 degrees. The limited output
is applied to a further trigometric function block 32, which
outputs a signal on lead 34 corresponding to the cosine of the
output signal from limiter 30.
A further divider 36 provides the quotient of the numerical angle
signal on lead 24 and the cosine signal on lead 34 as an output on
lead 38 to a rolling average filter 40. Filter 40 is synchronized
with the primary flight display indicator (not shown) to sample the
output of divider 36 at each display frame. From four to six such
samples are averaged and provide a signal representative of a
desired change in pitch attitude free of disturbances from
atmosphere turbulence. At each successive display frame a new
average is computed, with the earliest sample being discarded and
the newest sample computed in the average, to provide a "rolling"
output signal on lead 42 to further summing junction 44. Typically,
the update rate will be 200 ms for each successive display
frame.
A signal .THETA. representing the current pitch attitude of the
aircraft and derived from the inertial reference system 26 is
algebraically summed with the signal from filter 42 to generate a
pitch command signal .THETA..sub.CMD, which activates unique pitch
command symbology in the primary flight display indicator in a
manner to be described.
The present invention may be implemented using conventional analog
circuitry and computational techniques or by using conventional
wholly digital techniques or by using conventional hybrid
digital/analog techniques. To simplify the understanding of the
invention, it has been explained by using a generally analog format
as shown in FIG. 1, it being understood that the same analog format
may also represent, in block diagram form, the program of a
programmable digital computer wherein the various analog inputs are
converted to digital signals for digital processing and the various
outputs are converted to analog signals for driving the primary
flight display instrument.
The control law for generating a pitch display as described may be
defined by the following relationship: ##EQU2## where:
.PHI.=aircraft roll attitude, limited to + or -30.degree., in
degrees
.THETA..sub.CMD =commanded pitch attitude defining the upper and
lower pitch limits of the resolution advisory symbology, in
degrees
.THETA..sub.EXIST =current pitch angle, in degrees
V.sub.ZTCAS =TCAS vertical speed command, in ft/min V.sub.ZEXIST
=current vertical speed, in ft/min
V.sub.T =true airspeed, in knots
K=conversion constant
Referring now to FIG. 2 as well as FIG. 3 in which like reference
numerals indicate like components, the flight director display
instrument 50 includes an attitude directional indicator 52 having
an index 54 in the form of an aircraft symbol which is relatively
fixed with respect to the display field of view while the horizon
reference line 56 is responsive to the roll attitude of the
aircraft. Thus, in the example of FIG. 2, the horizon reference
line 56 is angularly displaced by 20.degree. in roll. A plurality
of reference marks 58 are displaced on the circumference of the
indicator 52 which indicate the roll attitude of the aircraft when
aligned with one of the reference marks 58. Note that the aircraft
symbol 54 remains stationary while the horizon line 56 moves with
roll of the aircraft. In a conventional manner, the display
includes an airspeed tape 60, an altitude tape 62, a horizontal
indicator 64, and a normalized angle of attack scale 66.
The attitude directional indicator further includes a second
plurality of reference symbols 68 which are substantially
orthogonally disposed with respect to the horizon line 56, and are
indicative of the pitch attitude of the aircraft. As can be most
readily appreciated from FIG. 2, the aircraft symbol 54 denotes a
pitch attitude of about 5 degrees above the horizon, the reference
marks 68 being indicative of 5 degree increments and being
numerically calibrated at 10 degree intervals. The aircraft
instrument panel includes a mode selector switch (not shown) for
engaging selected flight modes during which the indicator 50 would
be adapted to the mode being utilized. Thus, in the resolution
advisory mode an alphanumeric display 68 "RA ONLY" indicates to the
pilot that the attitude situation indicator 58 will provide pitch
command symbology assuming priority over any underlying
indicia.
The indicator 50 in resolution advisory mode includes first and
second indicia (70,72) superposed on the field of view. The indicia
70 comprises a horizontal band of a predetermined color, typically
green, disposed with respect to the vertical axis denoted by
reference mark 74 in accordance with the pitch angle signal
.PHI..sub.CMD derived from the resolution advisory command. It is
defined by a pair of upper and lower horizontal lines having a
vertical depth corresponding to a target range of acceptable pitch
deviation in accordance with the upper and lower bounds of the
resolution advisory command. The indicia 72 comprises a pair of
angularly disposed display lines 72a, 72b of a second predetermined
color, preferably red, and terminating at respective ends of the
first indicia 70 so as to form a symbol in the form of an
open-ended trapezoid. In FIG. 2 the open ends are downwardly
disposed, and indicate a command to climb to the pitch attitude
displayed by horizontal bar 70. The upwardly facing horizontal
green bar 70 is representative of the direction that the pilot is
commanded to move the controls so as to align the bar 70 with the
aircraft symbol 54. If a resolution advisory command directs a
descent, then the angular lines will be disposed with the open ends
above the horizontal bar.
There is further provided a vertical speed advisory tape and scale
80 which directly displays the resolution advisory vertical speed
command corresponding to the desired pitch command. A green target
band 82 indicates a commanded vertical speed corresponding to the
pitch bar 70. A red target band 84 indicates a proscribed vertical
speed range corresponding to the red guarded pitch band denoted by
lines 72a and 72b. Typical input parameters for the PFD display on
FIG. 2 are as follows:
______________________________________ Indicated airspeed 220 knots
Altitude 5500 feet MSL Roll attitude 20 degrees right bank Vertical
velocity-TCAS 1000-1500 ft/min green target band Vertical
velocity-existing 2400 ft/min descent Pitch attitude-existing 5
degrees up Pitch attitude-TCAS command 7 degrees up
______________________________________
Referring now to FIG. 3, there is shown a condition in which the
resolution advisory provides a warning of the presence of two
threat aircraft. This is indicated by presenting a third indicia 86
symmetrically disposed with respect to the vertical axis and
oppositely disposed with respect to the symbol defined by the first
and second indicia 70, 72a, 72b. Note that only one green target
bar 70 is presented, the third indicia being completed with a line
88. In the situation indicated, the aircraft is at a zero bank
attitude and pitched 5 degrees above the horizon line 56. A down
advisory for a first threat aircraft is indicated by the green
target bar 70 being located below the horizon line. Indicia 86
being downwardly pointed with respect to the base of its
trapezoidal infiguration indicates the response to the resolution
advisory with respect to a second threat aircraft, and would
preferably also be displayed as red lines to alert the pilot to the
minimum safe pitch to avoid collision with the second aircraft.
Vertical speed tape 80 here displays the green target vertical
speed rate 82 and is bordered by a red band 90 and a further red
band 84, the red bands 84, 90 denoting the proscribed vertical
speed rates to avoid collision with the threat aircraft, while the
green band 82 denotes the commanded vertical speed rate from the
TCAS computer. It will be appreciated that the pilot should avoid
climbing at a rate such that the tape numerical readout 92 remains
or enters into the red zones.
While the invention has been described in its preferred
embodiments, it is to be understood that the words which have been
used are words of description rather than limitation and that
changes may be made within the purview of the appended claims
without departing from the true scope and spirit of the invention
in its broader aspects.
* * * * *